Random number generation is an important aspect of many digital and electronic applications. For example, in the field of cryptography, random number generation is key to encryption algorithms. A random bit stream is a sequence of binary signals lacking discernible patterns or repetition over time.
In electrical circuitry, a random bit stream may be generated from a source that naturally exhibits random characteristics. For example, thermal noise on a CMOS device in the frequency range between 100 MHz and 1 GHz is generally known to be efficiently random.
However, generating a purely random bit stream based on a physical random phenomenon can be problematic. As known in the art, the mere act of sampling may interfere with the actual randomness of the random physical phenomenon being measured. For example, in order to ensure true randomness, the measurement circuitry cannot introduce any bias into the probability that the measured value will be translated to a binary 0 or a binary 1. For example, if a sampling circuit measures a voltage level of noise at a given moment in time and compares it to a known threshold generated by the sampling circuitry, process/voltage/temperature variations may cause a drift in the threshold value over time, which may skew the sampling circuitry to translate more sampled values to one bit value or the other. Thus, the process is no longer random since there is no longer an equal chance of sampling a “1” or a “0”.
Accordingly, a need exists for a technique for generating a purely random bit stream from a physical process. In particular, it would be convenient to generate the purely random bit stream from a naturally occurring randomness source within the circuitry itself. In addition, a need exists for preventing drift from pure randomness over time and across different manufactured circuits due to process/voltage/temperature variation.